Storage of biological and chemical samples is becoming widespread in biotechnological and medical industries. Many of these samples must be stored at or below freezing temperatures. Generally speaking, a regular freezer operates from about −5° C. to −20° C., an ultra-low temperature freezer operates from about −50° C. to about −90° C. (preferably at about −80° C.) and a cryogenic freezer operates from about −140° C. to −196° C. (boiling point of liquid nitrogen). For some applications, it is advantageous to store samples below about −120° C. For purposes of this patent application, the term “ultra-low temperature” shall mean temperatures below about −50° C. and above temperatures generally considered to be cryogenic.
Large automated sample storage and retrieval systems that store samples within one or more ultra-low temperature (e.g., −80° C.) or cryogenic (e.g., about −140° C. to −196° C.) freezer compartments are known. Biological samples stored in these systems are often contained in sealed plastic laboratory tubes or vials having a diameter of 3.5 mm or larger. Larger tubes are sometimes called vials in the art, but both are referred herein as tubes, storage tubes or sample storage tubes. The tubes or vials are typically held in storage racks having an array of tube receptacles, for example, 384, 96, 48 or 24 tubes and having openings in the bottom of the tube receptacles. In most cases, a two-dimensional barcode containing identifying information is adhered to the bottom of the storage tube and is able to be read through openings in the bottom of the tube storage racks.
A mechanical robot is often provided to place and retrieve the tube storage racks from the ultra-low temperature or cryogenic freezer compartment. The dimensions of the tube racks are typically SBS footprint compatible, but the tubes often have a variety of dimensions. The robot interacts with an I/O module in order to introduce samples into the system from the ambient environment and to retrieve samples for use outside of the system. The freezers typically have trays, shelves or cassettes for several hundred or even thousands of tube storage racks. It is not normally desirable to remove an entire SBS tube rack from the system through the I/O module when only one or a few tubes from a given storage rack are desired to be retrieved. The removal procedure may allow for the ingress of moisture into the system, and also renders the other samples held in the same tube rack susceptible to warming and thawing, at least partially, even if the tube rack is removed from the system temporarily. Robotic tube picking mechanisms are used in some systems to pick individual tubes for retrieval from the system. Even pulling storage racks from an ultra-low temperature or cryogenic freezer in order to pick tubes in a refrigerated, yet warmer environment, such as −20° C. or −30° C., can also allow undesirable warming of samples.
While tube picking mechanisms are generally known in the art, the environment within an ultra-low temperature or cryogenic freezer compartment is typically too cold to ensure reliable operation of conventional tube picking mechanisms. One issue is that the electrical, pneumatic and hydraulic components are unreliable at such ultra-low temperatures. Also thermal expansion and contraction of robotic components and storage racks can cause significant mechanical difficulties if not properly addressed. Another issue is that the formation of frost and ice is exacerbated due to the low moisture saturation point in ultra-low temperature or cryogenic environments. At such low temperatures, the air can hold very little moisture so any moisture introduced into the freezer environment tends to form frost on the cold surfaces within the environment. Frost and ice accumulation can interfere with the removal of tubes from racks and with the insertion of tubes into the racks. In addition, the moving parts of a tube picker in the freezer environment can become contaminated with ice and cause mechanisms to jam.
To date, tube picking mechanisms have been commercially used in low temperature (e.g. −20° C.) environments, but as mentioned it is difficult or impractical to operate a tube picking mechanism in ultra-low temperature or cryogenic environments. For this reason, some commercial systems compromise and place the ultra-low temperature or cryogenic freezers within a refrigerated −20° C. enclosure and pick sample tubes from the racks in the −20° C. environment. However, as mentioned previously, exposure of samples even to a −20° C. environment may cause undesirable warming.
The present invention is directed to tube picking mechanisms that are particularly well suited for use in an automated ultra-low temperature (e.g., −80° C. or −135° C.) or cryogenic storage and retrieval system. An object of the present invention is to provide a system that can efficiently and reliably pick selected tubes from storage racks within a tube picking chamber maintained at ultra-low (e.g. −80° C. or −135° C.) or cryogenic (e.g., about −140° C. to −196° C.) temperatures. Another object is to provide a system that also efficiently and reliably transfers tubes picked from retrieved source racks to a destination rack in an ultra-low temperature or cryogenic environment so that the selected tubes are ready for export from the system.